1. Technical Field
The present invention relates to a liquid supply apparatus and a liquid ejecting apparatus in which a pump is provided in the middle of a supply flow path which connects a liquid accommodating unit and a liquid ejecting head.
2. Related Art
For example, as an example of this kind of liquid ejecting apparatus, an ink jet type printer which performs printing by ejecting an ink (liquid) from nozzles of a recording head (liquid ejecting head) onto a medium such as paper (for example, refer to JP-A-2009-166473 (FIG. 1 and the like)) is widely known. An ink supply apparatus (liquid supply apparatus) which supplies an ink to the recording head from an ink cartridge (liquid accommodating unit) is provided in this kind of printer. For example, an ink supply apparatus in which a diaphragm type pump is provided in the middle of a supply path between the ink cartridge and the recording head is disclosed in JP-A-2009-166473 (FIG. 1 and the like).
Recently, although there is a case where an ink having relatively high viscosity is used, it is slightly difficult for a reciprocal pump such as a diaphragm type pump to reliably pump the ink having high viscosity in some cases. For this reason, a rotating type pump such as a gear pump capable of reliably pumping an ink is used in a printer which handles an ink having high viscosity. For example, a printer in which a gear pump (circulation pump) is provided in the middle of a flow path (circulation flow path) which connects a sub-tank and a recording head is disclosed in JP-A-2006-159811 (FIG. 6 and the like). In addition, an ink jet type printer in which an ink tank and a recording head are connected with the same number of plural flow paths as the number of ink colors and a gear pump is respectively provided in the middle of each flow path is disclosed in JP-A-6-328723 (FIG. 1, FIG. 2 and the like).
However, in a configuration in which a gear pump is respectively provided in the middle of each of the same number of plural flow paths as the number of ink colors which connect plural ink cartridges and a recording head, when a motor (power source) and a transmission gear are provided in every gear pump, the number of parts is increased and arrangement space and costs are increased. Therefore, it is preferable that plural gear pumps be driven with one common power source to achieve the decrease in the number of parts.
In this case, while the printer performs printing, all gear pumps usually rotate. Since the printer uses different ink based on the printing colors, it is not necessary to consume a predetermined amount for each color. Due to this, when the gear pump is driven at a rotation speed in accordance with color ink of a largely consumed amount, the ink pressure in an output side (discharge side) of the gear pump is excessively increased in ink where used amount is small. When the ink pressure in the output side of the pump is excessively increased, an ink ejection amount per dot is increased and color tones of a printed image are changed.
To solve such problems, for example, an ink supply apparatus in which a solenoid type clutch is provided between a power source and a pump (tube pump) is disclosed in JP-A-2009-51050 (FIG. 5, FIG. 7 and the like). In other words, a pressure sensor which detects the ink pressure in each output side (discharge side) of each pump provided in the middle of plural flow paths which connect ink accommodating units and a recording head and the solenoid type clutch which individually connects or blocks a power transmission path between the power source and each pump in every pump are provided in the ink supply apparatus. Then, when the ink pressure in the output side of the pump exceeds a threshold value, the clutch corresponding to the pump is shut off to stop the driving of the pump.
However, it is necessary to provide the pressure sensor which detects the ink pressure or the solenoid type clutch in every pump in the ink supply apparatus disclosed in JP-A-2009-51050 (FIG. 5, FIG. 7 and the like). For this reason, the number of parts is increased so that the structure of the ink supply apparatus is complicated and it is necessary that a control unit perform control to switch clutches according to detected the pressure of the pressure sensor for every pump. Therefore, there are problems in that the control of the ink supply apparatus is complicated and a burden on the control unit is increased.